Apparatus for reproducing images in color



P. H. WERENFELS ET AL 2,546,529

APPARATUS FOR REPRODUOING IMAGES 1N COLOR 2 Sheets-Sheet l Filed Oct.1l, 1951 P. H. wERENFr-:Ls ET AL 2,646,529

APPARATUS FOR REPRODUCING IMAGES IN COLOR Filed 001. 11, 1951 July 21,1953 2 Sheets-Sheet 2 5 mu W57. fw n ...LAL 1,.. O WE n f CM, y W7 .e wWW; www1, 1 A

, following manner.

Patented July 2l, 1953 APPARATUS non REPRODUCING minniey IN' COLORlPeter H. Werenfels, Lawrenceville, and James E.

Eckert,- Princeton, N. J., assignors to Radio Corporation of America, acorporation of Delaware Application october 11, 1951, serial NuzusioThis invention relates to improvements in apparatus for providing areversible rotating magnetic iield. This improved apparatus is to beemployed in conjunction with a cathode ray tube employing a single beamof electrons for sequen-f tially reproducing primary colors at anintensity c determined by signals applied toit.

A kinescope for reproducing images in color in response to electricalsignals has been devised in which the beam of electrons rotates aboutthe path to the target that it would follow in the normal kinescope. Therotation is produced by aradial rotating magnetic iield. Hou/ever, thebeam is focussed so that it strikes the same spot as a normal beam.Hence the beam can be thought ofas generating a surface of revolution ofnearly conical shape having its apex scanning the target. The rotationof the beam thus causes the electrons of the beam to approach the targetfromV constantly Varying directions in addition to the change indirection resulting` from the scanning action. The target is constructedso that the primary color emitted in response to the beam of electronsdepends on the direction of approach of the beam with respect to thepath that would be followed in a normal kinescope, wherein the beam isnot rotated, andthe changes in direction due to the beam scansion do notproduce any changes in color. The colors are therefore reproduced in agiven `sequence as the beam rotates. v e

As pointed out in the U. S. patent application bearing Serial No.220,622, and iled on April 12,. 1951, in the name of Sziklai, Schroederand Bedford, improved results can be obtained if the transmittedsignalrepresents the primary colorsl in one sequence during one intervalof time and a reverse sequence during another interval of time.

It has previously been suggested that the rotating magnetic field couldbe established in the Two pairs of diametrically opposed coils aremounted about the neck of the cathode ray tube in such fashion thattheir magnetic iields lie along a radius of the neck. The pairs of coilsare so disposed that their radial magnetic iields make an angle of 90with one another. Each pair of vcoils is energized with diierentlyphased currents of beam rotational frequency. If the coils are notcoupled together, reversal of beam rotation has been obtained Abyinterchanging the phases of the energizing currents applied to thedifferent coils. It hasalso been suggested that a rotating magneticiield can be set up if,v the coils are coupled together and s claims.(o1. 31e-.7.24)

li tl" 2l only one pair is energized directly. Whether this coupling isc'apac-itative or inductive depends on the direction of rotation to beemployed. The direction of rotation can also be' reversedV by directlyenergizing the other pair of coilsr Merely switching the directenergization from one pair oi coils to the other, although eiecting thedesired beam Vrotation produces 90 phase shift in the resultant magneticheld Consequently;l the beams direction of approach to the screenchanges and there is an undesirable change the color reproduced at thescreen of the cathode ray tube.

Accordingly, it is an object of the present invention to provide meansfor reversing the rotation o'k a radial magnetic field established bycoupled coils in such manner that Vthe instantaneous phaseof theresultant held is not changedv at the instant'when its direction ofrotation is reversed. e

Briefly, this objective may be achieved by energizing one pair ofcoils,v directly to produce a magneticeld rotating in one direction,'andenergizing the other pair of -coils by means of a Y phase shift-er toproduce an opp'ositely rotating magnetic field.

The manner in which this objective may be reached will bey betterunderstood from the detailed description of the drawings in which:

Figures land 1A illustrate the details of a color kinescope with whichthe present invention may be employed.

FigureA 1B illustrates the details of' a coincidence circuit that may beemployed',

Figure 2 illustrates a circuit embodying the invention to effect thereversal of rotation ofthe beam in the kinescope in Figures 1, 1A and 1BWithout change in the phase of the resultant field.

Figure Skillustra'tes thevphysical arrangement of the coils fof the yokeshown in Figure 2,

Figures 4 and 5 are vector diagrams useful in explaining the operationof' the beam rotation yoke of Figure 2, and l Figure 6 is a schematicdiagram of another ar-a rangement ofthe coils of the beam rotation yokeshown in Figure 2,.

Referring to the drawings, Figurel 1 shows a catho-deray tubeto be usedin conjunction with thel circuit of this invention. vThe tube consistsof an evacuated yenvelope l0, having both a conical portion l2' and atubular neck portion llicoaxi-'ally joined. together as shown. 'Iheconical portion i2 ofthe envelope: is closed by a faceplate [6 andiclosely spacedrfrom it is a iiuorescent( target and. screen structureyi8V tobe described below. Mounted coaxially within the tubular envelopeportion I4 is an electron vgun structure for producing and focusing abeam of electrons 20 on the screen structure I8. The electron gun is ofconventional design and consists of a cathode cylinder 22 closed, as isshown, at the end facing the target screen i8. The closed end of thecathode cylinder is coated, as is Well known in the art, by .a mixtureof strontium and barium oxides which, when heated to an appropriatetemperature, produce a free emission of electrons.

A control grid cylinder 24' coaxially surrounds the electron emittingend of the cathode 22 and has an apertured plate structure closing oneend thereof and closely spaced from the coated surface of the cathode. Ashield electrode or grid 26 constitutes Ya short thimble-like electrodehaving an aperture in the bottom thereof for the passage of electronstherethrough. Spaced along the tubular neck portion I4 and coaxial withthe other electron gunpartsis a tubular iirst anode electrodeV 28,having an enlarged-portion at the end facing the fluorescent screen I8.A second anode electrode is formed by a conductive rcoating 3G on theinner surface of the tubular envelope portion I4 and extends into theconical envelope portion I2 to a point adjacent the fluorescent screenI8. The several electrodes described, which constitute the electron gunstructure of the tube, are, during tube operation connected to a sourceof -direct current potential that may be a voltage divider 32 connectedbetween the positive and negative points of a direct current potentialsource.

The electrostatic fields produced respectively between electrodes 2B and28, and 23 and 30, are of a converging nature and `cause the electronsto form into a beam having a minimum cross section or cross-over point Bbetween tubular electrode 28 and screen I3. The electron beam, afterpassing through this cross-over point 55, tends to diverge beforestriking the screen I8. The diverged beam is bent away from the centralaxis of the tube by a rotating radial magnetic v eld. As is well knownin the art, lsuch a field can be generated by applying current of onephase to a first pair of coils 60 that are diametrically mounted aboutthe neck of the tube and applying current of a different phase to asecond pair of coils 60 that are mounted With their axis at 90 to thefirst pair. For simplicity the coils 60 and BG are shown as one yoke 5I.A focusing coil 34 serves to converge the electrons within the beam andalso to direct the beam to the same point on a mask 44 that the beamwould have struck if the coils 60 and 60 were not used. Thus the beamsubstantially generates a cone of revolution having an apex at the mask44.

The electron beam and hence the apex of the cone of revolution may 'becaused to scan over the surface of the mask 44 in any desired pattern orraster. However, in tubesof this type, the conventional scanningconsists of parallel lines from top to the bottom of the screen I8. Thescanning of the beam is produced by scanning iields established by twoypairs of scanning coils included in the yoke 4B. Each pair of coils isconnected to well known circuits 13 producing saw-tooth voltages forproviding both .line and frame scansion of the beam.

In the screen structure I8, themasking electrode 44 is positioned infrontjof a transparent phosphor` supporting sheet 45. The maskingelectrode 44 is formed from ,thin metallic foil which is opaque to theelectrons ofthe beam 2i).

in Figure 1A rit can be seen that if the electron beamapproaches thetarget from any one of the directions indicated as X, Y, or Z, theelectrons of the beam will pass through the vapertures of the maskingelectrode 44 and strike those phosphor spots which are in line with thebeam path coincident with these directions. When the beam approaches-thetarget along a path X it strikes only those phosphor coated spotsindicated by R, which luminesce with a red light. In a similar manner,whenthe beam approaches the target along path Y, it strikes only thoseareas indicated by the letters G which luminesce with a green light. Ifthe tube is a, three color tube, the electrons of the beam approachingthe target along the path Z will strike those phosphor areas indicatedby the letter B, which luminesce with 4a blue light.

Thus, the combined effects of the rotating field of coils 60 and BQ andthat of the focusing coil 34 results lin the beam 2!) being rstdisplaced from its normal path and then redirected along a new path tostrike the surface of target I8 at an angle of from sequentiallydifferent directions and accordingly strikes the phosphor spots 50 insequence.

The signals that sequentially represent the color in the scanned sceneare detected by any suitable receiver 52 and are applied to the controlgrid24 so as to vary the intensity of the kbeam Alternating current ofbeam rotational frequency is applied directly from an oscillator 64 to aswitching circuit 66. The output of the oscillator 64 is also vsuppliedto the switching circuit 66 indirectly via a 90 phase shifter B8.Details of suggested switching circuits that form a part ofthis-invention will be discussed in connection with Figures 2 and 3. Oneend of each of the coils 543 and 68 is grounded. The switching circuitacts to selectively connect the ungrounded ends of the coils 60 and '63to the oscillator 54 and the phase shifter 58 respectively.

If .the coils 6D and G0 are properly coupled,

the reversal of the'direction of rotation of the' resultant radialmagnetic eld established by the coils 60 and 5G' as well as thedirection of rotation of thejbeam 20 may be brought aboutby energizingone or the other.

In order that the beam 2l) be turned off as it is traveling from onecolor spot to the next, the third harmonic 'of the output of thesampling oscillator E4 is developed by 'a harmonic generator 'I andapplied to the cathode 24 in suitable phase and amplitude via a phasecontrol 'II and an amplifier 12. The positive peaks of this harmonickeying Wave overcome the 'beam cut off bias between the grid Z4 and thecathode 22 so as to key the beam on only when it strikes any single oneof the phosphor spots Ell.

When the signals applied to the grid 24 from the outputrof thereceiver52 represent a given primary color the beam 2li. should strikeV thephosphor spot that emits that color. In the system wherein the presentinvention is applicable, a burst ofl energy of color sequence or beamrotational frequency is inserted on the back porch of the televisionsignal at the transmitter. This energy of beam rotational frequency hasa xed phase relationship to the sequential change in Vcolor informationv.of the transmitted wave. `A separator 65 separates. the burst in amanner described in RCABulletinS on Color Television and UHF, October1949 to July 1959, and the burst is employed to control the phase of thealternating current supplied by the sampling oscillator 9,4 in any wellknown nia-nner. The phase of the burst may not be the same as thesignals representing a primary color, and any difference canv beaccommodated by the phase control l! so that the red spot of phosphor isstruck by the beamv when. the transfinitted signal represents red.Further details of the color synchronizingsystem are not in1 cluded asthey are not believed necessary to the understanding of the presentinvention.

The following. description relates to a Way of changing the polarityv ofthe-switching. circuit 59 and hence the direction of beam rotationbe.-tween successive elds. Horizontal and vertical denection waves arederived from 'the outputof the receiver 91 by standard deflectioncircuitsl and applied to thevhorizontal and vertical deflection coils inyoke 4G respectively. During beam retrace, rapidly collapsing magneticfields in the deflection coils produce voltage pulses of highamplitudeand in the opposite direction to the v deflection wavessupplied'by .the deflection ,circuits i3. If standard odd lineinterlaceisomployed, these horizontaland vertical flyback pulses occursimultaneously during the vertical blanking intervals of `every otherfield. The iiyback pulses are Yapplied to a coincidence circuit "i9 thatproduces a control pulse only when v.the pulses coincide. The controlpulse is applied to the source ofswitching voltages 15. This lattersource may be a free running multivibrator having two outputs that are180 out of phase. One phase is applied to the switching circuit 95 vialead 16 and the other is applied to the switching circuit 65 via lead11. When a pulse appears at the output of the coincidence circuit 1d themultivibrator 15 is triggered and the polarity of the signals appearingon leads i5 and 11 reverses.

One type of' coincidence circuit that may be used is illustrated inFigure 1B. A multigrid tube 18 is biased to out off by placing apositive potential on its cathode as shown. The horizontal ilybackpulses are applied to a grid '59 by ordinary .RC coupling. The verticalflyback pulses are differentiated by an RC coupling network 89 beforebeing applied to a grid 8i. Whenv the two flyback pulses occursimultaneously the cut off bias on the cathode of the tube 18 isovercome on both grids and a pulse appears at its plate. It is thispulse that triggers the bistable source 15. The oppositely phasedoutputs of the source i5 are applied to the switching circuit 95 vialeads 16 or 11 as noted above.

The switching circuit that` is the subject of the present invention isillustrated in detail in Figure v2. The sampling frequency supplied bythe oscillator 66 is applied to an input terminal 83 and is coupled tothe grid 84 of a switching amplifierl 85 via a condenser 89. The plate81 of the amplifier 95 is coupled to the ungrounded terminals of a pairof beam rotation coils 88 and 89. A variable condenser 90 is connectedin parallel with the beam rotation coils 88 and 89 and is adjusted sovthat the parallel combination thus formed is resonant atthe samplingfrequency.

The input .terminal 83 is also coupled to the grid 9| of anothernormally cut-oi switching amplier 92 via a phase shifter 93. The plate94 of the amplifier 92 is coupled to the ungrounded ends of another pairof beam rotation coils 95 and 96. A variable condenser 9'1'is coni.-nected in parallel with the coils 95 and 99 and is adjusted to tune themto parallel resonance at the sampling frequency.

The ungrounded ends of the beam rotation coils 88 and 89 are criticallycoupled-by means of a variable condenser 98 to the ungrounded ends ofthe beam rotation coils 95 and 96. The beam deection coils 88, 81, 95,96, the condensers `99 and 91 and the coupling condenser 98 form thebeam rotation yoke 6L The switching amplifiers and 92 are biased to cutoff 'by the potentiometers 99 and 100 that are connected to the ends ofthe grid leak resis-A tors I9I and H12 that are connected to theV grids84 and 9! respectively. The lower ends of the resistors IDI and |02 varealso connected to the leads 1.6 and 11 from the source of switchingvoltages 15. Graphs |03 and |05 illustrate the rela.- tionship betweenthe switching voltages that may appear on the leads 16 and 11. If 'theswitching voltage or the lead 19 is at its most positive point theamplifier 85 is rendered conductive. At the same time the switchingvoltage on the lead 11 is at its most negative value and the switchingamplifier 92 remains cut off. When the values ci the switching voltagesis intcichanscd, for erg ample during the next .eld, the amplifier 95 isout ol and the amplifier 92 is rendered conductive. l

mounted 0n opposite sides of the neck I4 so as to produce a horizontalmagnetic cld; the coils 95 and. 96 .are mounted on opposite Sides cf theneck I4 so as to establish a vertical magnetic field. If the magneticfields are precisely cut ci phase and if stray magnetic clds areneglected. there is nc magnetic cimicling between thc coils. of thedifferent pairs. Hence the only coupling available is by Way ci thecondenser 93..

That the phase shifter 93 should change the phase of the samplingvoltage S that is applied to it by substantially 90 can be seen by theaid of the vector diagrams of Figures 4 and 5. If the amplifier 85 isconducting, the current Hi in the coils 88 and 89 that produce thehorizontal magnetic field lags the sampling voltage S by 90. Due to thecapacitative coupling provided by the condenser 9B, the current Vi inthe coils 95 and 96 that produce the vertical magnetic field is the samephase as S. If the sampling voltage S is applied directly to thevertical coils and 99, the vector relationships between the coil or eldcurrents Hi, Vi and the sampling voltage S are as illustrated in Figure5. The Vectors Vi and Hi are interchanged in position and accordinglythe direction of rotation of the magnetic field is reversed. When thesampling wave S is applied directly to the horizontal field coils B3 and89 the diagram of Figure 5 shows that the resultant magnetic field isvertical as only the vector Vi has any projection on the horizontal orreal axis; the vector Hi is imaginary and has no real component. Whenthe sampling wave S is applied directly to the vertical coils 95 and 95,the vector diagram of Figure 6 shows that the current in the horizontalcoils 85 and 86 is a maximum and that the current in the vertical coils95 and 96 is zero. In the case of Figure 5 then there is a verticalfield and in the case of Figure 6 is a horizontal field. Hence changingthe direct application of the sampling or beam rotation voltage from oneset of coils to the other changes the position of the resultant magneticfield by As shown in Figure 3, the coils 88 and 89 are produces anundesired changein the color produced by the tube. In accordance withthis invention, the phase shifter 'i3 compensates for the phase shift sothat the resultant magnetic eld has the same position regardless'of theswitching tube that is conductive. y

Figure 6 illustrates another Way in which the yoke 60 may beconstructed. The horizontal eld coils 8g, 89 and the vertical eld coilsk95, 96 are separately connected in series and each is tuned by arseparate variable condenser.

What is claimed is:

1. Apparatus adapted to establish a rotating magnetic eld comprising incombination an input terminal to which a desired alternating voltage maybe applied, a rst pair of coils having one end coupled to said inputterminal, and the other end grounded, a condenser in parallel withsaid'rst pair oi coils, .a second pair of coils having one end grounded,a condenser in parallel with said second of coils, said condensershaving 'such capacitance that the parallel circuits formed by them andthel coils are resonant at substantially the frequency of thealternating voltage applied to the input terminal, a phasesuch'capacitance that the parallel circuits formed by them and the coilsare resonant at substantially the frequency of the alternating voltageapplied to the inputlterminal,` a phase shifter coupled between saidinput terminal and the ungrounded end of said second pair of coils, acondenser coupled between the ungrounded ends of said rst and secondpairs of coils so as to critically couple them together.

3. Apparatus for reproducing images in color comprising in combination acathode ray tube, an electron gun mounted in said tube, a rst pair ofeld coils adapted to establish a magnetic eld in a given plane, a secondpair of eld coils adapted to Aestablish an intersection magnetic eld insaid plane, means for supplying said each pair field coils withdifferently phased alternat ing currents of like frequency so las toestablish a rotating magnetic field so as to bend said electronsawayfrom a normal path along a radius determined by the direction of saidrotating magnetic field, means for bending said electrons back towardsaid normal path, a target mounted so as to intercept said beam ofelectrons at a pointV where said beam intersects said normal path, saidtarget being adapted to emit light Of a different primary colordepending on the direction of approach of said beam with respect to itsnormal path, and switching means adapted to interchange the phases ofthe altern-ating currents applied to said pairs of eld coils.

, PETER H. WERENFELS.

JAMES E. ECKERT.

References cited in the fue ofV this patent UNITED STATES PATENTS NumberName Date 2,052,338 Budenbom Aug. 25, 1936 2,454,378 Forgue Nov. 23,1948 2,522,055 OBrien p ri sept'. 12, 195o

